It is known that aromatic polyamide-imides that are excellent in the balance of mechanical properties and heat resistance can be obtained by polycondensation of aromatic tricarboxylic anhydrides or their derivatives with aromatic diamines. However, aromatic polyamide-imides that have hitherto been generally proposed are unsatisfactory in that they are poor in melt moldability and will partially decompose under some molding conditions. To improve the moldability, various methods have been suggested such as the following:
1. A method that uses aromatic diamines having an ether linkage as disclosed in Polymer Preprints, 15 (1), page 761 (1974).
2. A method that improves the moldability by copolymerization as disclosed in Japanese Laid-Open Patent Application No. 91724/1983.
However, these methods are practically not satisfactory in view of the balance of moldability, heat resistance and mechanical strength that are taken into consideration as a whole.